1. Priority and Field of the Invention
The present invention relates to a system and method for detecting and locating an acoustic event. More particularly, but not by way of limitation, in a system for identifying and locating an acoustic event, the present invention provides an acoustic sensor which operated with improved electrical efficiency.
2. Background of the Invention
Gunfire and sniper detection systems are generally known in the art. Such systems can be broadly grouped into three categories: systems which pinpoint the precise location of the source of gunfire; azimuthal sensors which provide an indication of the radial direction to the source of gunfire; and proximity sensors which merely provide an indication that nearby gunfire was detected. While such systems have been demonstrated to perform well in both law enforcement and military applications, the entire field is presently an emerging technology.
In many large cities, gun-related violence has become a plague of epidemic proportions. Urban gunfire, whether crime-related or celebratory in nature, results in thousands of deaths per year in the United States alone. Gunfire location systems, such as those installed in the Redwood City, Calif., Glendale, Ariz., Willowbrook, Calif., City of Industry, Calif., and Charleston, S.C. areas, have proven to be effective in reducing law enforcement response time to detected gunfire, apprehending criminals, collecting evidence, and reducing the occurrence of celebratory gunfire. One such system is described in U.S. Pat. No. 5,973,998, issued to Showen, et al., which is incorporated herein by reference.
Showen, et al. discloses a system wherein sensors are placed at a density of roughly six to ten sensors per square mile. Audio information is sent to a computer at a central location and processed to: detect a gunshot; determine a time of arrival for the gunshot at each sensor; and calculate a location of the shooter from the differences in the times of arrival at three or more sensors. Showen, et al. takes advantage of the long propagation distance of gunfire to place sensors in a relatively sparse array so that only a few of the sensors can detect the gunfire. This permits the processor to ignore impulsive events which only reach one sensor—a concept called “spatial filtering.” This concept of spatial filtering radically reduces the sensor density compared to predecessor systems, which require as many as 80 sensors per square mile.
Another gunshot location system is described in co-pending U.S. patent application Ser. No. 10/248,511 by Patterson, et al., filed Jan. 24, 2003, nw U.S. Pat. No. 6,847,587 which is incorporated herein by reference. Patterson, et al., discloses a system wherein audio information is processed within each sensor to detect a gunshot and determine a time of arrival at the sensor. Time of arrival information, as determined from a synchronized clock, is then transmitted wirelessly by each sensor to a computer at a centralized location where a location of the shooter is calculated in the same manner as in the Showen, et al. system.
As yet, azimuthal systems have not been as widely accepted as, for example, the Showen, et al. system. Azimuthal sensors typically employ one or more closely-spaced sensors, where each sensor includes several microphones arranged in a small geometric array. A radial direction can be determined by measuring the differences in arrival times at the various microphones at a particular sensor. Presently such systems suffer from somewhat limited accuracy in the determination of the radial angle, which in turn, translates into significant errors in the positional accuracy when a location is found by finding the intersection of two or more radial lines, from corresponding sensors, directed toward the shooter. Since errors in the radial angle result in ever increasing positional error as the distance from the sensor to the source increases, the reported position will be especially suspect toward the outer limits of the sensors' range.
Under certain conditions, power consumption of an acoustic sensor is of concern. For example, in a military application it may be desirable to provide a soldier-worn sensor to identify sniper locations. Such a sensor would obviously require a portable supply of electrical power, most likely batteries. Since size and weight are major considerations in a wearable, or carryable, device, the electrical efficiency of the sensor dictates the size and weight of the required batteries.
Power consumption may be of major concern in fixed sensor as well. In general, anywhere that AC power from an electric utility is not available, the alternatives for electrical power, i.e. solar, battery, etc., dictate a need to maintain an awareness of electrical efficiency. It is known in the art to use telephone lines to return acoustic information to a host computer and to use electrical power available over the phone line to power a sensor. As will be appreciated by those skilled in the art, only a few milliamps of electrical current are available from a telephone line to power circuitry.
It is thus an object of the present invention to provide a system and method for improving the electrical efficiency of a remote acoustic gunshot detection sensor.